1. Field of the Invention
The present invention relates to a developer dispersing device which can be used, for example, for dry two-component development. The invention is applicable to electro-photographic apparatuses, such as copiers, printers, facsimile machines, etc.
2. Discussion of the Background
A typical electrophotographic apparatus is illustrated in FIG. 20 and comprises a photoconductive drum 2 as a charge receiving member and a charging device 1. The photoconductive drum 2 rotates at a predetermined speed in the direction indicated by the arrow sequentially in relation to a plurality of processing stations disposed about its rotational path of movement. As illustrated in FIG. 20, the charging device 1 initially contacts the surface of the photoconductive drum 2 at a predetermined pressure and charges the photoconductive drum 2 to a substantially uniform potential, either positive or negative. Downstream at exposure device 3, light rays reflected from an original document are reflected through a lens and projected onto a charge portion of the surface of the photoconductive drum 2 to selectively dissipate the charge thereon. Such selective charge dissipation records an electrostatic latent image on a circumference of the photoconductive drum 2 corresponding to the informational area contained within an original document.
Thereafter, the photoconductive drum 2 rotates downstream to a developing device 4 where a developer mix (for example carrier particles and toner) are passed into contact with the latent electrostatic image. The toner particles are attracted away from the carrier beads by the latent electrostatic image to thereby form toner powder images on the surface of the photoconductive drum 2. The development station may apply one or more or colors of developer material.
Also illustrated in FIG. 20 is a paper copy sheet 5 which is advanced into contact with the development latent image at a transfer device 6. The toner powder image is thereafter transferred from the photoconductive drum 2 to the paper 5. After transfer, the toner image is fixed on paper 5 by a fixing device 7, and photoconductive drum 2 is discharged by a discharger device 9. Residual toner on the photoconductive 2 is removed by a cleaning device 8.
FIG. 21 illustrates in detail the development device 4. In FIG. 21, a toner hopper 10, a dispersing roller 11 and a developing sleeve 12 are illustrated. Toner is supplied into the toner hopper 10 by rotation of a toner supply device 15. This supplies toner onto the dispersing roller 11 which supplies toner to the developing sleeve 12. FIG. 21 also illustrates a doctor blade 13 for controlling the quantity of toner on the developing sleeve 12 as well as a developing area 14.
In conventional arrangements, a lateral difference of toner density in the dispersing roller 11 causes an unevenness of image density on a copied paper. When an original document comprises a lateral difference of image ratio or information ratio and the original document is copied a plurality of times, some parts which have a high image ratio or a high information ratio consume a lot of toner, and this causes the toner density of these parts to become extremely lower than the toner density of the other parts.
Accordingly, dispersing rollers not only have to have the function of mixing newly supplied toner with stock toner, but also have to have the function of pumping up the toner and also laterally or longitudinally dispersing toner. If a dispersing roller does not correctly longitudinally or laterally disperse toner, the toner supplied to the dispersing roller will form a lump or the like. This will cause an unevenness of image density. Accordingly, a dispersing roller which not only longitudinally disperses toner, but also shakes and mixes the toner, is necessary.
An example of a conventional screw-type dispersing roller is illustrated in Japanese Document 55-6997. Although the dispersing roller in Japanese Document 59-6997 achieves a lateral transfer of toner, the mechanism is expensive and requires a maximum amount of space. Additionally, it does not achieve the desired amount of radial and lateral toner movement which is necessary to achieve an even image density.
FIGS. 22 and 23 of the present application also illustrate conventional dispersing devices in the form of dispersing plates or wings. Both types of toner dispersing devices illustrated in FIGS. 22 and 23 can achieve some form of lateral toner transfer between cells 160, however, utilization of only the plates 170 cannot assure a positive transfer of toner between cells. In the toner transfer devices illustrated in FIGS. 22 and 23, toner is transferred from one cell to another via a gap between the plates and the hopper. If the plates 170 are large, toner transfer between cells is difficult, while if the plates are small, the mixture of toner is not sufficient. Also, these types of devices do not provide the desired combination of radial and lateral transfer of toner.
Finally, Japanese documents 64-24282 and 3-105370, which also disclose conventional toner dispersing devices, illustrate devices which are not capable of achieving a sufficient lateral transfer of toner in combination with a radial movement of toner for achieving an even image density.